The present invention relates to bicycle sprocket assemblies and more particular to a sprocket assembly including a lightweight sprocket carrier and a plurality of sprockets having stepped rivet holes configured to receive a rivet shaft, a rivet head and a riveting tool.
Typically, a sprocket assembly for a bicycle having a derailleur gear system includes multiple sprockets that are supported, concentrically with decreasing diameters, by a sprocket carrier. For example, DE 199 37 212 A1 discloses a sprocket assembly that includes a plurality of sprockets attached to a stepped four-arm sprocket carrier. The largest sprocket supports the sprocket carrier and each step receives a sprocket. The largest sprocket and sprocket carrier are nonrotatably mounted to the wheel hub for transferring the torque of the other sprockets to the wheel hub. The other sprockets are attached to the sprocket carrier or the largest sprocket by rivets.
Another sprocket assembly is disclosed in the Utility Model DE 296 23 671 U1 that includes two sprocket subassemblies. Each subassembly includes a hub and carrier arms extending radially outward from the hub. Two sprockets are attached to each subassembly, one on each face of the carrier arms, using the same rivets. A difference between a number of teeth on the two sprockets is small. Spacers are used to individually attached several other sprockets to the bicycle hub.
Due to the desire to have a large number of sprockets, resulting in close gear ratio spacing with small differences in sprocket outside diameters, and the desire to have a lightweight construction, several drawbacks are associated with the above sprocket assemblies. One drawback with tight axial arrangement of individual sprockets on the sprocket carrier is projecting rivet heads that protrude into the space between the sprockets and interfere with the chain. Another problem is the damage to the sprocket surface caused by the riveting tool during the riveting process. Therefore, there is a need for skillful arrangement and attachment of multiple sprockets on a sprocket carrier.